Purification and separation of dicarboxylic acids



United States Patent O PURIFICATION AND SEPARATION OF DICARBOXYLIC ACIDS Leo S. Pooler, Chicago, Ill., assignor to The C. ltpHall .Company of Illinois, Chicago, 11]., a corporation of Ohio No Drawing. Application June 21, 1950, Serial No.. 169,542

. 6 Claims. (Cl. 260537) This invention relates to the purification of dicarboxylic acids produced from the oxidation of saturated, unsaturated and substituted fatty acids. It includes-the use of the dichlorobenzenes (either -pure substances or a mixture of the isomers) for the separation and purification of these acids.

PREPARATION OF DICARBOXYLIC ACIDS The dicarboxylic acids showninthe example intthis disclosure are acids which have 'been produced by .the oxidation of cottonseed fatty acid (largely 'lineolic and oleic acids), oxidized in a mixture of dilute nitric .acid (8 to HNOs) in the presence of excess air,.under approximately ten pounds persquare inch gauge pressure at a temperature of 234 F.-all of which iscovered in patent application by George R. Murphy; Serial No. 169,065, under dateof June 19, 1950.

While the acids of. the example were produced as'outlined above, nevertheless this invention covers the purification and separation of dicarboxylic acids of whatever source, and I do not limit this invention to those dicarboxylic acids produced by the air-nitricacid' oxidation method. By fatty acid in this disclosure, I-do not limit myself to saturated monocarboxylic .acids but I include unsaturated and substituted acids astheyare generally considered to be in the fatty acid field. Such monocarboxylic-acids include thc'mixedfatty acids derived from linseed oil, soybean. oil, castor oil, coconut oil,-cottonseed oil, peanut oil, tall oil, sunfiowerseed oil, rapeseed oil, mustardseed oil,.-safiiowerseed oil, corn oil; sea animal oils including fish oils; anima1-'oils,-such as tallow, lard, oil, etc.

When the foregoing monocarboxylic acids are oxidized by nitric acid the product in the water phase may contain, amongother things, the following:

a. Monocarboxylic acids such as pelargonic acid and lower molecular weight fatty acids.

17. Aldehydes.

c. Semialdehydes (a monocarboxylic. acid with the terminal CH3 oxidized to the aldehyde), also called half aldehydes.

d. Dialdehydes.

e. Odd-numbered carbon dicarboxylic acids.

Even-numbered carbon'dicarboxylic acids.

g. Nitric acid and oxides of nitrogen.

h. Water PURIFICATION AND SEPARATION OF DICAR- BOXYLIC ACIDS The purification ofdicarboxylicaacids is covered to some extent in the U. S. patent applications of Roger L.

Logan,'-Se1'ial"'No. 57,370, filed October 29, 1948, now

abandoned (but see Logan 2,662,908) and George 'R. Murphy, Serial No. 169,065, filed June 19, 1950. Certain improvements have been made in the purification of crystals (Cut No. 1).

2,716,133 Patented Aug. 23, 1955 process not covered by either of the two foregoing inventions. The invention disclosed here describes these improvements.

The water phase, containing mixed dicarboxylic acids as well as all the impurities previously listed (a, b, c, d, g, and h), is evaporated so that the solids content of the solution is increased to between 60% and while being blown vigorously with air to effect further oxidation.

The dicarboxylic acid solution is then delivered to the crystallizer where it is cooled slowly to develop large crystals, after which the slurry is filtered and the crystals are washed. The mother liquor, is returned to the reactor for further oxidation. Small amounts of dicarboxylic acids are found in the mother liquor.

shown by the following example:

Example To 500 pounds of crude dicarboxlic acids crystallized from the aqueous reaction product from such nitric acid oxidation were added 1250 pounds of dichrorobenzene (86% ortho and l4% para). The batch was then heated to 273 F. in order to dissolve the dicarboxylic acids. The solution was then cooled to 2l0-215 F. in about one hour and then centrifuged to secure the first cut Seventy-two pounds of crystals were recovered which had an equivalent weight of 58.8.

The solvent solution was then cooled slowly to F. and the second cut of crystals was procured (Cut This cut amounted to 96 pounds with an equivalent weight of 64.8. This equivalent .weight indicates that this is a mixture of succinic and adipic acids.

The mother liquor was'then cooled to 68 F- and the 'third cut (Cut No. 3) of pounds, with an equivalent weight of 77.9, was obtained.

The third cut (190 pounds) was taken up in 110 pounds of water, first, to remove the remaining dichlorobenzene and, second, to separate the more water-soluble dicarboxylic acids (succinic and adipic) from the less watersoluble acid (suberic). The dichlorobenzene was removed from the batch by steam distillationwhich removed not only the dichlorobenzene but also the remaining traces of nitric acid. The batch was cooled to 100 F. and portion No. 3 (a)106 pounds, with an equivalent weight of 84.3was removed. The mother liquor was then cooled to 65 F. This gave portion No. 3 (b)- 30' pounds, with an equivalent weight of 72.3.

The analysis of cut'No. 3 (a) was found to be:

78.0% suberic acid 20.0% adipic acid 2.0% azelaic acid This'analysis gave a calculated equivalent weight of 84.39 against the 84.3 reported above.

To 65 pounds of Cut No. 3 (a) 'dicarboxylic acids were added 430 pounds of Water. The batch was heated to 190 F. It was then cooled slowly to 67 F. Forty-five pounds of. dry acids were obtained. This batch (No. 3 (a) 1) showed anequivalentweight of 83.6.

The 45 pounds of acids from the previous crystallization (No. 3 (a) 1) were dissolved in 334 pounds of water at 212 F. and the batch was cooled to 80 F. and approxi- V mately 28 pounds of acids were obtained with thefollowing analysis:

CUT NO. 3 (a) 2 97.0011% suberic acid 2.00% azelaic acid 0.50% adipic acid 0.40% non-volatile 0.20% monobasic acid (as C9) 0.02% ash in non-volatile Cut'No. 1 was reworked as follows: To 72 pounds of dicarboxylic acids'were added 110 pounds of water. Five pounds of nitric acid were added and the batch was heated to 100 C., filtered to remove foreign matter, then allowed to cool and the resultant crystals were recovered by filtration. Forty-two pounds of dicarboxylic acid were procured having an equivalent weight of 59.0;' Pure succinic acid has an equivalent weight of 59.045. This material when analyzed was found to 'be 98.9% 'pure' which was higher in succinic acid than some C. P. succinic acid 1 V with which it was compared.

The remaining filtrates were collected for reworking. A material balance was not run. The example is offered to show that by the use of water, and a non-polar solvent such as dichlorobenzene it is possible to separate'suberic acid and succinic acid from the batch of mixed dicarboxylic acids and thus secure a high grade technical product in each case.

The dichlorobenzene used in the foregoing illustration, while not pure ortho,-is the dichlorobenzene of commerce.

I do not limit myself to its use but my invention applies to mixtures of the isomers, ortho, meta and para. It is inconvenient to use para dichlorobenzene alone because of its high melting point. Higher chlorinatedproducts of benzene may be used but since they are still higher in molecular weight they have higher boiling points than dichlorobenzene and hence offer a little more difliculty in regeneration of the solvent for reuse.

The dichlorobenzene which has been used for several batches is highly contaminated. When it is felt that the dichlorobenzene can no longer be used because of containination, it is passed through a steam stripping column and the nitric acid and the dichlorobenzene are distilled off. The residue is returned to the reactor for further oxidation, together with the dicarboxylic acids which had 4 been dissolved 'in the dichlorobenzene. The dichlorobenzene is used again and again for the separation and purification'of mixed dicarboxylic acids.

'Dilute nitric acid was employed in the final clean-up of the acid crystals since iron, copperand nickel were present as impurities from piping and equipment. 'Withj 'out-the use of nitric acid the finished dicarboxylic acid had a green to brown color from metal contamination while with nitric acid in the water. solution, these metal salts'were converted to soluble nitrates and were removed from the product, giving a good looking product low in V ash content.

The process of separation and purification outlined here, as a method of purification applying to crude dicarboxylic acids, applies equally well to a product after preliminary purification and to material from other sources than that of air-nitric acid oxidation. While I have used the nitric my example, I do not limit myperatureacid thus crystallized from the solution and adda '4 ing a minor per cent of nitric acid thereto, and then cooling this aqueous solution to a relatively low temperature and thereby crystallizing dicarboxylic acid of shorter chain length therefrom.

2. In the purification of dicarboxylic acids in solution in non-polar solvent and contaminated with salt of metal from the class consisting of iron, copper and nickel which comprises crystallizing dicarboxylic acid from said solution together with said salt, preparing from the crystalline mass an aqueous solution containing dilute nitric acid, and then crystallizing dicarboxylic acid from the aqueous solution while leaving the metal salt in solution in the mother liquor. I

3. The process of separating dicarboxylic acids of different chain lengths from a crystalline mixture containing succinic, adipic and sube'ricacids, which comprises dissolving the mixture in dichlorobenzene with heat, cooling the resulting solution to obtain three crystalline fractions, the first of which is largely succinic acid and the last of which is largely suberic acid, dissolving these two respective fractions separately in water and separately crystallizing therefrom succinic acid and suberic acid, each in a relatively high state of purity. V I

4. The process of the preceding claim in which the crystalline starting material is contaminated with a salt of a metal of the class consisting of iron, copper and nickel, and in one of the. recrystallizations from water using dilute nitric acid whereby said metal salt remains dissolved in the aqueous mother liquor resulting from said crystallization, whereby the metals are separated from the crystallizeddicarboxylic acid and the dicarboxylic acid is substantially free from such. etal salt.

5. The process of treating a crystalline mixture of succinic, adipic and suberic acids and recovering one of said acids therefrom substantially free of the other two acids, which comprises dissolving the crystalline mixture in dichlorobenzene with heat, thereafter, cooling and obtaining a crystalline fraction which contains the desired acid and no more of the other twoacids than is readily soluble in water, and then by crystallization from water obtaining v the desired acid substantially'fre'e from the other two acids.

6. The process of separating two ,dicarboxylic acids of different chain lengthsfrom a crystalline mixture of thetwo, the. first of said acids being of the class consisting of succinic and adipic acids and the second acid being of the class consisting of adipic and subericacids, which comprises dissolving the mixture in a dichlorobenzene, then cooling and thereby separating from the solution a. crystalline fraction, then further cooling the resulting dicblorobenzene solutionand obtaining a second crystalline fraction containing a mixture of the first and second acids, dissolving this fraction in water with heat and then by cooling the resulting aqueous solution separating the second acid'while leaving in the aqueous mother liquor substantially all of the first acid present in the fraction.

References Cited in the file of this patent UNITED STATES PATENTS Coleman Nov. 8, 1932 2,300,955 Meier Nov. 3, 1942 2,343,534 Cavanaugh et al Mar. 7, 1944 2,352,547 Jenkins June 27, 1944 2,365,290 7 Price .et-al Dec. 19, 1944 2,369,036 Y Fitzpatrick et al Feb/6, 1945 2,420,938 Doumani et al May 20, 1947 2,557,282 Hamblet et a1 June 19, 1951 2,560,156 Cavanaugh et al. July 10, 1951 2,603,667 Pankratz et a1 July 15,1952

OTHER REFERENCES MacArdlei Solvents in Synthetic Organic Chemistry,

Van Nostrand, p. 135 (1 925.). 

1. THE PROCESS OF RECOVERING DICARBOXYLIC ACID FROM A SOLUTION OF LONGER AND SHORTER CHAIN DICARBOXYLIC ACIDS IN A DICHLORO BENZENE, WHICH COMPRISES COOLING THE SOLUTION FROM A RELATIVELY HIGH TEMPERATURE AT WHICH AT LEAST A PART OF THE ACID OF SHORTEST CHAIN LENGTH IS CRYSTALLIZED FROM THE SOLUTION WHILE RETAINING ACID OF LONGER CHAIN LENGTH IN SOLUTION, DISSOLVING IN WATER AT A RELATIVELY HIGH TEMPERATURE ACID THUS CRYSTALLIZED FROM THE SOLUTION AND ADDING A MINOR PER CENT OF NITRIC ACID THERETO, AND THEN COOLING THIS AQUEOUS SOLUTION TO A RELATIVELY LOW TEMPERATURE AND THERBY CRYSTALLIZING DICARBOXYLIC ACID OF SHORTER CHAIN LENGTH THEREFROM. 